Lance Tiernan, 18, was found not guilty of murder Thursday in the beating death of 16-year-old Anthony Parker, but they convicted him of the lesser charge.

Prosecutors played a video in the trial showing Tiernan slamming Parker to the floor, and said Thursday that the assault was no accident.

"This was an attack, an ambush, whatever it is, but this is one-sided carried out by this defendant here, a physical attack on Anthony Parker," assistant prosecutor Brad Burress said Thursday.

Tiernan testified that he never intended serious harm to Parker. He said he became angry when Parker told him no one cared about his problems and insulted his mother during a discussion about holiday plans.

Authorities said Tiernan assaulted Parker on Dec. 19 at One Way Farm, a group home where both lived. Parker later was taken to a hospital, where he died Dec. 28 of head injuries.